1. Field of the Invention
The technical scope of the invention is that of safety and arming devices for a pyrotechnic train of a projectile and namely micro-machined safety and arming devices.
2. Description of the Related Art
Safety and arming devices (or DSAs) are well known. They generally incorporate a screen blocking a transmission channel which connects a detonator and a pyrotechnic charge.
The screen is thus positioned across the transmission channel of the detonic wave between the detonator and charge and it prevents the latter from functioning.
One of the problems encountered with classical devices is their volume. The parts are relatively massive to be able to ensure the interruption of the pyrotechnic train. Motor means enabling the screen to be displaced must therefore be powerful. More often than not it is springs that are used and which remain tensed during the storage phases, which can lead to the deterioration of their mechanical properties and to a loss of reliability of the armament.
For several years it has been proposed to manufacture all or part of safety and arming devices using chips incorporating micro-machined or micro-engraved electro-mechanical elements, either in an element deposited on a substrate, or directly on the substrate itself. This technology, known as MEMS (Micro Electra Mechanical System) enables micro-mechanisms to be manufactured implementing a technique similar to that used to produce electronic integrated circuits.
U.S. Pat. No. 6,964,231 discloses such a micro-machined safety and arming device incorporating a shutter carrying a pyrotechnic charge and sliding through the action of the centrifugal force. This shutter is itself immobilized by a lock that is retracted via the projectile's acceleration upon firing.
Another swiveling lock enables the shutter to be released and to be moved into its arming position through the centrifugal inertial force. The swiveling lock is activated by a gas-generating pyrotechnic composition whose ignition is controlled by electronic means.
Such as safety and arming device thus enables two independent environmental conditions to be exploited to ensure arming: the longitudinal firing acceleration and the centrifugal acceleration. This double safety enables this device to be compliant with the most stringent standards with respect to projectile arming safety (STANAG 4187).
It is however complex in structure and namely the second lock (swiveling lock) requires the implementation of a pyrotechnic composition and means to ignite it. Electronics must therefore be provided to activate the functioning of this MEMS, which is thus poorly adapted to use in medium caliber ammunition (caliber of less than 50 mm) in which there is limited available space.
Patent EP2077431 proposes a micro-machined safety and arming device in which arming is fully mechanical and fulfils the most stringent safety conditions, namely those requiring the presence of two independent environmental conditions in order to move into the armed position.
This safety device also suffers drawbacks, however.
It incorporates a centrifugal counterweight that ensures a lock is held in an indentation in the shutter. The retention of this lock by the counterweight during the full stroke of the latter generates friction which disturbs the counterweight's movement, and thus the delaying of the centrifugal arming operation.